This invention relates to the processing of silver halide photographic materials. In particular, the invention simplifies chemical processing and reduces the volumes of liquid processing solutions employed. It applies to transparent film and reflection print materials, both colour materials and black and white materials. It is particularly useful where early stages in the processing sequence produce little or no effluent.
Normally, silver halide materials are processed in equipment with deep tanks containing processing solutions. The solutions need to be maintained in a chemically stable state to the extent that uniformity and consistency of photographic results are assured.
The effects of evaporation, interaction with atmospheric gases such as oxygen and carbon dioxide, and the effects of processing usually have to be compensated for by replenishment techniques. This requires operator intervention and/or the provision of additional solutions and means of adding them accurately. Also, liquid effluent is produced which has to be disposed of in a safe and cost-effective way. These wet chemical systems are generally difficult to keep clean.
Most currently used processes for silver halide films and papers involve several deep-tank stages including the development step, a bleach step where metallic developed silver is usually converted to silver halide, and a fixing step where the silver halide remaining undeveloped and any silver halide formed by bleaching is dissolved using a substance capable of complexing with silver ions to produce a soluble silver compound. This is usually washed out of the processed material in a washing or stabilisation stage. Sometimes the bleach and fix steps are combined. In the case of most black and white materials the bleach step is avoided.
Photographic colour paper materials usually use silver halide in sufficient quantity to produce all the oxidised developer in the process of development which is necessary to produce sufficient dye for satisfactory image densities. Low silver materials have also been described which use small fractions of the amount of silver needed to provide the image dye via, for example, reaction with colour-forming couplers. These low-silver materials are processed in the presence of oxidising agents such as hydrogen peroxide in so-called Redox Amplification or RX processes. In such processes the developed silver image is used to catalyse in an image-wise manner, the production of oxidised developer and hence, image dye. Such materials are appropriate for the production of prints.
It is possible to leave the developed silver in the image with little effect on image quality when very low amounts of silver halide are used Research Disclosure September 1997 p.638). In some circumstances it is actually desirable to leave the developed silver in the image areas. For example, a simpler process can be used when the bleach step is avoided. Also, it may be useful to leave silver in the image so that it can be used with automatic image detection systems which use infra-red light to detect the image.
It has also been suggested that it is possible to leave the silver halide in non-image areas. This retained silver halide can be stabilised to degradation by light for example by destroying the silver halide spectral sensitising dyes by exposure to light (U.S. Pat. No. 5,441,843) or by converting the silver halide to a more stable form such as silver iodide (U.S. Pat. No. 5,246,822).
There is still a possibility however, that degradation of non-image areas and those areas of low density can be degraded by atmospheric sulphur compounds which may convert the halide into the highly coloured silver sulphide over time so some eventual degradation to sulphide must be anticipated. This limits the amounts of silver which can be tolerated in the resulting colour images, i.e. it limits the amounts coated unless it can be removed. It is known that reductions in the number of silver centres and hence, dye clouds which contribute to image density lead to dye hue being degraded and image graininess being increased (G. B. Evans et. al., Proceedings of the ICPS Symposium, Antwerp, September 1998, p149). For high quality images where these effects are small or negligible, sufficient image centres must be used. This means that without reductions in silver halide crystal sizes which would lower photographic speed, sufficient silver must be used to provide the necessary number of image centres.
Image transfer materials are known in which undeveloped silver is solubilised by fixing agents and deposited from solution in the presence of the developing agent, onto nuclei which catalyse the conversion of silver ions to silver metal. This process is used to produce positive silver images in the material to which the silver ions are transferred (xe2x80x9cThe Theory of the Photographic Processxe2x80x9d ed. James, T. H. H., 4th Edition p 471).
Photographic processes usually involve a final washing stage to remove dissolved xe2x80x9cfixedxe2x80x9d silver and other materials which would cause images to be modified over time, particularly by increasing density in low density areas.
Lamination methods have been described in which silver halide is solubilised and transferred from the processed photographic layers to the lamination material where it can be trapped as a result of a chemical process. For example, U.S. Pat. No. 5,478,703 discloses that the silver can exchange with metallic aluminium in a fixer sheet to form silver metal and release aluminium ions. It also discloses that the fixer sheet may contain substances which can react with and immobilise or render harmless colour developing agents, oxidised colour developing agents and bleaching agents.
Wet chemical systems of processing are complicated by the means necessary to maintain them at a consistent performance level. Also, they are difficult to keep clean. They produce liquid effluent which requires disposal. Typical photographic processes consist of several treatments in different chemical baths plus a washing or stabilisation stage which is used to remove chemicals which would, if remaining in the image, modify the image over time. The majority of the effluent comes from the wash stages.
The problem to be solved is to provide a means of processing photographic materials in a simple process which minimises or eliminates liquid effluent while ensuring the removal of chemicals which would otherwise modify the images over a period of time. These include not only the organic materials such as colour developer but preferably also unreacted silver halide.
Removal of chemicals using a receiver sheet releasably laminated to the developed photographic material is desirable. In particular, the removal of organic chemicals e.g. developing agent from the photographic material without requiring a substance in the receiving sheet which will chemically react with it in order to immobilise it or render it harmless would be desirable.
The present invention provides a method of producing a photographic image in an imagewise exposed photographic material comprising one or more silver halide emulsion layers which method comprises
developing the material with a developer solution containing a silver halide developing agent,
releasably laminating the material with a receiver sheet containing an adsorbent for the developing agent in oxidised and unoxidised form, and, after a period of time sufficient for adsorption of the developing agent in the receiver sheet,
separating the photographic material and the receiver sheet.
The invention allows removal of developing agent from the processed photographic material using a receiver sheet which does not require the presence of a substance capable of reacting with the developing agent. The adsorbent used in the invention provides a simpler, less expensive means of removing the developing agent.
In preferred embodiments, the invention avoids the consequences of retaining silver halide in the image and in particular avoids the means, which would otherwise be necessary, of ensuring that the silver halide is not subsequently modified in a way which degrades the image.
The invention also provides a means of trapping silver removed from the imaging material thus providing a convenient means of silver recovery.
The use of RX chemistry may allow very low levels of coated silver whose presence in the image areas as silver and non-image areas as silver halide are tolerable. If photographic speeds are to be maintained at a practical level, such levels of silver result in increased graininess and degraded colour reproduction. This invention allows silver levels sufficient to ensure high quality images to be achieved without the need for a fixing stage and wash stage to be provided by immersion in tanks of solution while still ensuring good image stability.